After the storm came the drought. This was a contest that featured a seven-goal avalanche inside 34 minutes but then fell barren, yet was still unmissable and had Sir Alex Ferguson branding the experience "agony".

If it was the kind of pell-mell exchange all managers hate and neutrals love, the first-half count should have actually been eight – to break the record for an opening period – but Robin van Persie's strike near the break was ruled out wrongly.

For Ferguson a near-perfect day, in which Chelsea lost and Manchester City drew, ended with Manchester United's lead extended to three points before next Sunday's derby at the Etihad Stadium.

He told ESPN: "It was agony. The worst defending of this season and we needed to do something about it. We're needing to rescue the situation all the time. Fortunately we have players who can do that."

To call this the direst performance from a rearguard that had previously conceded the first goal 13 times in 21 matches in all competitions illustrates how manic an evening this was. To Ferguson's chagrin, his team contrived to take this tally to 14 as the breathless 26 minutes into which all seven strikes were compressed began.

Eight minutes had been played when this chronically leaky United defence allowed Jay Tabb to turn the ball to Jobi McAnuff. He swung in a cross, Jonny Evans's header went straight to Hal Robson-Kanu and his volley beat Anders Lindegaard via a deflection from the defender.

The first of United's two equalisers came when Michael Carrick found Anderson, who moved the ball on to Ashley Young, and when the Brazilian took the return he blazed a rocket of a shot past Adam Federici. Anderson's celebration featured a kind of strutting tap-dance on the spot.

That was after 13 minutes. Within 90 seconds Wayne Rooney gave the visitors the lead. From the Liverpudlian's corner Evans controlled the ball and, as he brought it down, Tabb decided to barge him over. Rooney beat Federici from the penalty spot.

Now came two Reading goals, each unmarked headers from corners delivered by Nicky Shorey.

This was simple, schoolboy stuff but United could do nothing to repel either. First Shorey's 19th-minute delivery found Adam Le Fondre and as Rio Ferdinand went wandering the No9 finished. Then Sean Morrison produced a carbon copy, rising to meet Shorey's kick to give Reading a hardly credible 3-2 lead.

By the time the clock showed 34 minutes it would be 4-3 to United, and Rafael had first been booked, then hooked by Ferguson (on 28 and 31 minutes, respectively), with the Brazilian apparently ignoring his manager's conciliatory gesture to embark on a sulky pout he still wore on half-time.

Of this reaction, the Scot said: "The boy was disappointed coming off. He has been one of our best players this season. I brought Chris Smalling on, which was an improvement in terms of height."

When the sides walked off for the break, what would prove United's winning advantage had derived from two slick moves. A Patrice Evra ball to Young became a one-two when the winger executed a backheel to his skipper, whose cross allowed an unmarked Rooney to slot a second.

Then Rooney created Robin van Persie's 13th of his debut United season. Carrick's pass was flicked sideways by the forward and the Dutchman, with his right boot, slid the ball beyond Federici.

Rooney, who ended with two goals to stretch his total to five, said of the goal glut: "It was crazy. It was end to end and I think we played some good attacking stuff but defended badly on set-pieces. We showed big character to see the game out. We're not happy about it [falling behind first, again]. If it keeps happening it will cost us. We need to try and get in front early and make it easier for everyone."

Although that was it for the period and match, Van Persie's case for a second appeared copper-bottomed: replays showed his finish was good before Adrian Mariappa cleared.

Rooney was in no doubt: "It certainly was over the line. It is difficult for officials to see because it is so quick. But I'm sure in the future there will be technology."

After Ferguson's pre-match exhortation to Rooney to score more, it had been a surprise to see him on the right of the 4-2-3-1 decided upon by his manager.

Yet, as with Van Persie, he was required to defend as Ferguson's midfield shield of Carrick and Darren Fletcher continued to struggle to slow this open game down.

Ferguson added: "There is a natural determination about the players. I just think we need to get the defending right from set-pieces. If we defend like that against Manchester City, I might need to play myself."

For Brian McDermott, whose side remain second-bottom, this was another case of so near yet so far: "It was a fantastic effort."